Osburn OB04010K Installation And Operation Manual page 41

6.3.5.6 R Calculations
The use of an R value is convenient when more than one material is going to be used in the hearth
extension to cover the combustible surface. This is because R values are additive, whereas K values are not.
To find the corresponding R factor to use for some selected materials, please see Table 1 : Thermal
Characteristics of Common Floor Protection Materials*.
There are two ways to calculate the R factor of the floor protection. First, by adding the R-values of the
proposed materials or if some K and thickness values are given, by converting them to R values.
To calculate the R factor for a composite floor protection made of a combination of alternative materials,
simply add the R-values of those materials. If the result is equal to or larger than the required R value, the
combination is acceptable. For R-values of some selected materials, see Table 1 : Thermal Characteristics of
Common Floor Protection Materials*.
Example: If the required floor protection R is equal or higher than 1.00. Proposed materials: four inches of
brick and one inch of Durock® board:
Four inches of brick (R = 4 x 0.2 = 0.8) + 1 inch of Durock® (R = 1 x 0.52 = 0.52). 0.8 + 0.52 = 1.32
This R value is larger than the required 1.00 and is therefore acceptable.
In the case of a known K and thickness of alternative materials to be used in combination, convert all K
values to R by dividing the thickness of each material by its K value. Add the R values of your proposed
materials as shown in the previous example.
In the previous example: Four inches of brick (K = 4/5 = 0.8) + 1 inch of Durock® (R = 1 / 1.92 = 0.52). 0.8 +
0.52 = 1.32.
Table 1 : Thermal Characteristics of Common Floor Protection Materials*
MATERIAL
®
Micore 160
®
Micore 300
®
Durock
®
Hardibacker
®
Hardibacker 500
®
Wonderboard
Cement mortar
Common brick
Face brick
Marble
Ceramic tile
Concrete
Mineral wool insulation
Limestone
Ceramic board (Fibremax)
Horizontal still air** (1/8")
HORIZON – Installation and Operation Manual
CONDUCTIVITY (k)
PER INCH
0.39
0.49
1.92
1.95
2.3
3.23
5.00
5.00
9.00
14.3 – 20.00
12.5
1.050
0.320
6.5
0.450
0.135
RESISTANCE (R) PER INCH
THICKNESS
2.54
2.06
0.52
0.51
0.44
0.31
0.2
0.2
0.11
0.07 – 0.05
0.008
0.950
3.120
0.153
2.2
0,920**
41